Lower back and neck pain is oftentimes attributed to the rupture or degeneration of intervertebral discs due to degenerative disk disease, spondylolisthesis, deformative disorders, trauma, tumors and the like. This pain typically results from the compression of spinal nerve roots by damaged discs between the vertebra, the collapse of the disc, or the resulting adverse effects of bearing the patient's body weight through a damaged, unstable vertebral structure. To remedy this, spinal implants have been inserted between vertebral bodies to restore the structure to its previous height and conformation and stabilize motion at that spinal segment.
Surgical treatments to restore vertebral height typically involve excision of the ruptured soft disc between two vertebrae, usually with subsequent insertion of a spinal implant or interbody fusion device to fuse and stabilize the segment. Spinal implants or interbody fusion devices have been used to fuse adjacent vertebral bodies since the 1960's. Currently, spinal implant devices are comprised of either allograft materials, natural, porous materials such as coral, or synthetic materials. A major drawback associated with allograft devices is the risk of disease transmission. Further, since companies that provide allograft implants obtain their supply from donor tissue banks, there tend to be limitations on supply. Synthetic devices, which are predominantly comprised of metals, such as titanium, also present drawbacks. For instance, the appearance of metal spinal implants on x-ray tends to have an artificial fuzziness, which makes assessment of fusion (one of the clinical criteria of a successful interbody fusion device) very difficult. Moreover, synthetic materials of this type (metals) tend to have mechanical properties that are unevenly matched to bone. Coral and other natural materials generally perform poorly.
Accordingly, there is a need in the art for a synthetic spinal implant material that does not carry the risk of disease transmission as with allograft materials.
There is also a need for a synthetic spinal implant material with a radiopacity similar to bone. A radiopacity similar to bone would allow for visualization of the implant between the vertebrae to assess radiographic fusion without distortion.
Further, there is a need for implants with mechanical properties similar to that of bone that can share the physiologic, dynamic compressive loads rather than shield them.
Moreover, there is a need for implants that are comprised of a material that bonds directly to bone and is bioactive.
In addition to the material limitations associated with existing implants on the market, there is also a need to provide spinal implants that are anatomically shaped with proper geometry and features to prevent expulsion or retropulsion. The term “expulsion” as used herein relates to the migration of the implant device in a forward (or backward) direction from the intervertebral space. Moreover, there is a need for a device with an increased surface area to allow for optimal contact with the cortical bone to prevent subsidence or sinking of the implant into each adjacent vertebra. There is a need to provide an implant that is bioactive with an open geometry for packing with graft materials that allows enhanced fusion between the endplates of adjacent vertebrae both via the bioactive surface of the implant and a preferred graft-packed opening.